Make volume button behavior always default to 'none.'

This was partially fixed by commit 220d80aff9549e156c58.
The app would default to none until the user entered
the settings, at which point default would change to 'dismiss'

Change-Id: I67a6064457403eeebbcd54ff6c4977a3c6321cb3

res/xml/settings.xml

@@ -45,6 +45,6 @@
         android:entries="@array/volume_button_setting_entries"
         android:entryValues="@array/volume_button_setting_values"
         android:summary="@string/volume_button_setting_summary"
-        android:defaultValue="2" />
+        android:defaultValue="0" />
 
 </PreferenceScreen>